Presidential Lecture by Robert D. Holt

The Value of Long-Term Experiments in Ecology

The Kansas habitat fragmentation experiment, 40 years old and counting.

Habitat destruction and fragmentation is one of the primary drivers of the current extinction crisis. There is a huge literature based on observational analyses of anthropogenically fragmented landscapes, and considerable mathematical ecological theory, but relatively few experiments.

One such experiment was initiated at the University of Kansas field station in 1983, to examine how fragmentation might affect the rate and pattern of secondary succession. This talk will provide a retrospective overview of this large-scale, long-term ecological experiment, and related theoretical explorations in spatial ecology and food web ecology. I will discuss why, on 'a priori' theoretical grounds, one might expect patch size and distance from source pools to influence successional trajectories, in plant communities and the consumer food webs they support. I will then explain some of the design considerations that figured into the eventual spatial configuration of the Kansas experiment, then delve into some of the key findings from this experiment.

In the first decade, there were many effects, often counterintuitive, of patch size on plant and consumer populations, but no overall effect on plant succession. After this initial lag, there was a pronounced effect of patch size and distance from sources on development of woody vegetation, an effect which grew with time. Early successional species showed intriguing patterns in their extinction dynamics. In recent years, the effect of patch size on local plant species richness has dramatically increased. The seminar will conclude by pondering the issue of whether or not this striking effect arises from spatial dynamics (as in island biogeography and metacommunity theory), or if, instead, reflects other more subtle effects of fragmentation on the abiotic environment and the web of species interactions. A general conclusion is that effects of fragmentation on populations and communities varied over time -- there appears to be a complex interplay of landscape structure, succession, and trophic interactions, in this system. This is likely to be generic, across fragmented landscapes.

The Kansas system illustrates how many ecological processes involve LONG transients, and so will be missed in short-term or ‘snapshot’ studies.

Robert D. Holt

Eminent Scholar and Arthur R. Marshall Jr. Chair in Ecological Studies, University of Florida

Robert D. Holt is an ecologist particularly known for theoretical and conceptual contributions to population and community ecology, and for fostering the integration of ecology with evolutionary biology. His research examines how species interact, both directly and indirectly, in complex webs and he addresses the ecological and evolutionary consequences of such interactions, and how such interactions unfold across space, contributing for instance to geographical range limits. He was born and raised in Tennessee. He graduated from Princeton in 1973 with a degree in physics, but fortunately each semester took for fun an upper-level course in biology. This allowed him to pursue graduate studies in biology at Harvard, where he received his doctorate in 1979. He then moved to the University of Kansas, where he was on the faculty and a curator in the Museum of Natural History. In 2001 he shifted to the University of Florida to take the titles of Eminent Scholar and Arthur R. Marshal Jr. Chair in Ecological Studies. He is a Fellow of the American Academy of Arts and Sciences as well as the National Academy of Sciences, and has been president of the American Society of Naturalists. He is a keen naturalist and has participated in expeditions to many remote corners of the globe.

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